Theory Of Operation

EVAP SYSTEM COMPONENTS
CALLOUT	DESCRIPTION
1	Filter - Fresh Air Inlet
2	Filter Hose (Filter to ESIM)
3	Evaporative System Integrity Monitor (ESIM)
4	Evaporative Canister
5	Canister Tube (Fuel Tank to Canister)
6	Purge Tube (Purge Solenoid to Canister)
7	Purge Solenoid
8	Manifold Hose (Purge Solenoid to Engine Manifold)
9	Recirculation Tube (Fuel Tank to FTPS)
10	Fuel Tank Pressure Sensor (FTPS)
11	Recirculation Tube (metal portion) (FTPS to Fuel Filler Tube)
12	Gas Cap or Cap-less Refueling Unit (if equipped)
13	Fuel Filler Tube
14	Multi-Function Control Valve (MFCV) in the Fuel Delivery Flange
15	GVV Tube (GVV to MFCV)
16	Grade Vent Valve (GVV)
17	Fuel Tank
18	Inlet Check Valve (ICV)
19	Hose - Fuel Filler Tube to ICV

EVAPORATIVE SYSTEM OVERVIEW: 

The Powertrain Control Module (PCM) monitors the Evaporative Emission System operation. The two main areas being monitored are the integrity of the system against leaks and the ability of the system to get fuel vapor from the canister to the Intake Manifold. The basic strategy used is that in a sealed system  , pressure will naturally increase or decrease in relation to temperature. As temperature increases, so does pressure inside the system. And conversely, as temperature decreases, pressure in the system will decrease as well and will eventually turn into a vacuum if no leaks are present. Even the smallest of leaks can be accurately detected in this manner. The ESIM has multiple functions. There are two weighted seals that keep the system normally closed from the atmosphere. The weighted seals are used to maintain the system pressure between +1 inch of water and -2 inches of water. Anytime (engine-on or engine-off) that pressure or vacuum reaches these thresholds, the weights will lift and provide relief. There is also a vacuum actuated switch that closes when the vacuum reaches a calibrated value. This is beneficial because the induced vacuum during a subsequent declining temperature will achieve the switch closed (pass threshold) sooner than if the tank had to decay from a higher built up pressure.

ESIM SWITCH STUCK CLOSED MONITOR: 

At ignition off, the state of the ESIM switch is evaluated. If the switch is open, a pass flag will set so the PCM power down process can complete. If the switch is closed, the PCM will wait a calibrated delay time and open the Purge Solenoid. In a normally functioning system, this will relieve the vacuum in the Fuel Tank by drawing in air from the atmosphere from the Intake Manifold. When the switch opens, a pass flag is set and the PCM will power down. If the ESIM switch does not open, after a calibrated time, an error is detected and a switch stuck closed failure event is set. Two consecutive failed events will mature a fault.

SMALL LEAK MONITOR:  This is an accumulative monitor and the data from each valid event is recorded and added to the previously recorded events. The PCM timer records the engine on/drive cycle and engine off time for each small leak monitor event. For an event to be valid the PCM must see;

1. An engine on/drive cycle for a minimum of 2 minutes.
   NOTE:

   The Engine on timer is clipped to a maximum of 26 minutes on any given trip.

2. And, when the engine is shut down, an engine off timer starts. There is a 12 minute delay time in which the PCM will ignore ESIM Switch input. The engine off timer period will continue to count until one of the three conditions exist:
   NOTE:

   At the next key on cycle a determination is made as to whether the event was valid and the information is kept.